Because one is English and the other is explicitly Japanese? Come on, that's not even a difficult question to answer. Hell, it's not even true onomatopoeia: Japanese has a LOT of words for sounds that aren't actually sounds. Onomatopoeia for smiling is damn weird.

[quote]"Typical woman, really: too weak to fight her own battles, so she surrounds herself with boot-lickers." Gütta spoke with a sneer nestled into the wrinkles of his nose, bleeding down into the corners of his mouth. "Beyond that, we haven't met much."[/quote]

... did you... totally misunderstand the setting? Blatant sexism like that... doesn't fit. Particularly in this order of all places. Plus... half the cast. I mean one second there's Japanese not-onomatopoeia and the next, uh... "let's assume Victorian gender roles".